System, method, and apparatus for forming a patterned media disk and related disk drive architecture for head positioning

ABSTRACT

A solution to the problem of long, e-beam mastering times needed for patterning masters for patterned magnetic disk media is disclosed. A process for fabrication of masters takes advantage of the circular symmetry of magnetic disks and reduces the total required mastering time by an order of magnitude over prior art processes. This process relies on e-beam mastering of one small arcuate portion of the master, and then replicating that portion around a circular path on the master several times to create a full disk master. The architecture of this design also corrects for errors in head positioning on the final patterned media disk that may be introduced by the mastering process.

BACKGROUND OF THE INVENTION

This divisional patent application claims priority to and the benefit ofU.S. patent application Ser. No. 11/066,665, filed Feb. 25, 2005.

1. Technical Field

The present invention relates in general to manufacturing patternedmedia and, in particular, to an improved system, method, and apparatusfor patterned media disk nanoimprinting and a related disk drivearchitecture for head positioning.

2. Description of the Related Art

In future hard disk drives, it is expected that all magnetic mediahaving an areal density greater than 1 Tb/in² will require patternedmedia. Known manufacturing processes for making patterned media rely onfabrication of a single, complete master that is replicated many timesto create whole replicas. Upon deposition of magnetic material, thereplicas become actual patterned media disks that are used in readingand writing information. Typically, the replication process relies on“nanoimprinting” or stamping. The patterned surface on the master isused to imprint on a polymer on an imprinted substrate. The patterncreated in the polymer is then permanently transferred to the imprintedsubstrate using conventional manufacturing processes such as wet and dryetching, metal lift-off, etc. It is also common to form several wholestampers from the single master and create many replicas from eachstamper.

Due to the small feature sizes (smaller than 25 nm), the masters willlikely have to be fabricated by using high resolution e-beamlithography. E-beam lithography is a very precise but slow process thatmay require hundreds of hours to generate masters. This represents amajor portion of the time and cost needed to create masters. Inaddition, mastering processes that require this much time may sufferfrom overall, e-beam system instability over the long periods of timeand may therefore be unmanufacturable even if the cost associated withlengthy mastering times was affordable. Thus, an improved solution formanufacturing patterned media would be desirable.

SUMMARY OF THE INVENTION

Embodiments of a system, method, and apparatus for forming a patternedmedia disk and a related disk drive architecture for head positioningare disclosed. The present invention creates a full area patterned mediamaster by (1) first creating a sub-master in the form of “pie slice”that contains approximately 10% of the area of the full patterned masterusing, for example, e-beam lithography or other high resolution methods(e.g., x-ray lithography, ion beam lithography, etc.); (2) stamping(e.g., nanoimprinting) the full area of the master with the sub-masterand repeating the nanoimprinting in a circumferential direction aroundthe master; and (3) providing a hard disk drive system architecture forcorrecting head positioning errors that may result from this process.

For example, one embodiment of the head positioning correction processmeasures and stores positioning errors between each two adjacentsections and uses those values for correction of the head position.Significantly, the process also creates an additional dedicated servo(head-positioning) field for each sub-section. These additional fieldsare used to correct remaining radial position shifts that are smallerthan, for example, one-half data track. In addition, the full areamaster created by this process may be used to create several stampersfor creating actual patterned media disks.

In one embodiment, the present invention comprises a method of patternedmedia disk nanoimprinting and a related disk drive architecture for headpositioning. The method comprises creating a portion of a sub-masterpattern; developing resist and using other manufacturing processes tocreate a sub-master based on the portion of the sub-master pattern, thesub-master comprising only a section of a full area master; using thesub-master as a pattern to form all sections of the full area master;transferring the pattern of the full area master into a mastersubstrate; and providing a dedicated servo section that is used forcorrection of radial track positioning errors between sections.

The foregoing and other objects and advantages of the present inventionwill be apparent to those skilled in the art, in view of the followingdetailed description of the present invention, taken in conjunction withthe appended claims and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the features and advantages of theinvention, as well as others which will become apparent are attained andcan be understood in more detail, more particular description of theinvention briefly summarized above may be had by reference to theembodiment thereof which is illustrated in the appended drawings, whichdrawings form a part of this specification. It is to be noted, however,that the drawings illustrate only an embodiment of the invention andtherefore are not to be considered limiting of its scope as theinvention may admit to other equally effective embodiments.

FIG. 1 is a series of schematic diagrams depicting one embodiment of ananoimprinted media disk and a related disk drive architecture for headpositioning constructed in accordance with the present invention;

FIG. 2 is an enlarged diagram illustrating an e-beam patterned sectorsub-master and nanoimprinted master;

FIG. 3 is a further enlarged diagram illustrating one embodiment ofdata, servo, and correction fields for a subsection;

FIG. 4 is a further enlarged diagram illustrating tilt of a subsection;and

FIG. 5 is a high level flow diagram of one embodiment of a methodconstructed in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, one embodiment of the present invention isdepicted. Initially, one section of a sub-master pattern 21 is createdusing a high resolution technique. Following e-beam lithography,development of resist and other manufacturing processes (such as metallift-off, etching, etc.) are used to create the sub-master 23. Thesub-master 23 is used to create a full area master 25. The sub-master 23is stamped or nanoimprinted repeatedly into polymer on the surface ofthe master substrate a number of times (e.g., for “M” sections) in acircumferential direction around the master substrate. Followingnanoimprinting of the polymer, the pattern imprinted in the polymer istransferred into the master substrate using, for example, dry etching,wet etching, or metal lift-off. Each subsection 27 contains an equalnumber of servo sectors 29 that are used for head positioning and datasectors 31 that contain patterned media bits. At the beginning of eachsubsection 27 there is a “dedicated servo” sector 33 that is used forcorrection of radial track positioning errors smaller than one-halftrack width.

The total time to pattern an entire master 25 with e-beam lithography isgiven by T_(total). If the full area of the master 25 is divided into Msubsections 27, and if the time required for stamping or nanoimprintingone section 27 is T_(s), the time needed to create the full area master25 is described by the following equation. The present inventionsignificantly improves total mastering time by a factor of M. Forexample:new time=T _(total) /M+M*Ts, where T_(s)<<T_(total) (T_(s) is negligiblewhen compared to T _(total)).

FIG. 2 describes one embodiment of an approach to nanoimprinting of themaster 25, including: (a) nanoimprinting even-numbered sections 23 afirst and then transferring the nanoimprinted polymer pattern into thesubstrate by using dry or wet etching or metal lift-off; and (b)nanoimprinting odd-numbered sections 23 b into polymer and transferringtheir pattern into the substrate. This approach minimizes the errorsthat may result due to flow of the nanoimprinting polymer at theboundary of the sub-master, or at the boundary of one stampedsubsection.

The right side of FIG. 1 illustrates the layout of each of thesubsections. Each nanoimprinted subsection 27 has: (a) data fields 31that contain patterned media bits; (b) servo or head positioning fields29 (labeled “s₁”) that are similar in nature to present-day servo fields(i.e., contain gain control, servo synchronization mark, cylinder code,and fine positioning or positioning error signal information); (c)special servo fields 33 (labeled s₂) that are used to correct headpositioning errors smaller than one-half data track. Each of thesubsections may be offset from its ideal position in a radial direction(i.e., relative to an axis of rotation of the disk), an angulardirection (i.e., displaced along the circular track), or rotationallytilted. All these errors must be measured and corrected by the proposedservo architecture.

When a full area master is created by nanoimprinting subsection master Mtimes in the circumferential direction, the cylinder code values in eachof the s, sectors will not be lined up along the circular track due toradial direction errors (Δr) and tilt errors (Δγ). In this case, amemory table is formed (stored in the disk drive ROM) with dimensions ofM rows by N columns. Each row j represents radial errors present on thej-th subsection at N point from ID to OD (practical value for N is ofthe order of magnitude of about 10). These radial errors are allmeasured relative to the same base values, which may be defined by thefirst nanoimprinted subsection. After all these values are stored in thetable, it is easy to keep the cylinder position in each of thesubsections accurate by simply correcting by the error value stored inthe table. However, after correcting for the cylinder value, there is aremainder error that is smaller than one-half track, which is the reasonfor the additional servo field s₂.

In addition to the radial error it is also possible to introduce angularerror (Δφ) along the circular direction. Angular error introduces servosampling synchronization problems. Currently, the window for detectingSAM (characteristic signature of servo field that turns on servo everysample) is approximately 2% of one sampling time. For example, if thetrack pitch is 25 nm, the estimated number of sectors required is about500 to 1000 for a one-inch drive. Assuming a one-inch drive and 3600rpm, the maximum value for angular error along the circular directionis: 360/1000*0.02=26 arc sec. This value may be reasonably achieved bygood mechanical positioning of the sub-master during subsectionnanoimprinting and should not represent a difficulty.

FIG. 3 shows that the maximum allowed radial positioning error duringmastering is defined by the disk area real estate lost at the far endsof the ID and OD due to the mismatch. Before cylinders stop matchingeach other due to the radial shift, there may be a significant loss ofreal estate. If acceptable real estate loss is approximately 0.2%(delta_rmax=½×(rOD−rID)×0.002, which is approximately 6 microns in thecase of one-inch disks. This value also may be controlled by carefulpositioning of the submaster during nanoimprinting of subsections.

FIG. 4 illustrates a subsection 27 that was imprinted with built-in“tilt error” as shown by arrow 34. Without any correction schemes, theposition shift per sector caused by tilt should be less than 5 to 10% ofthe track. This value may be reasonable enough and may be achieved byprecise mechanical positioning of the sub-master. Alternatively, thevalue of tilt needs to be measured for each subsector. This may be donewith a single measurement per subsector if radial shift is alreadymeasured. Once tilt is known, a table is created with target PES valuesfor N zones (approximately 10) inside each subsector. This tablerequires approximately 16×10×1000=160 kbits). The feed-forward schemewith closed loop servo would be used, which is similar to RRO correctiontoday.

The one-half track error may be corrected in several ways. The s₂ fieldmeasures the actual position of the head and provides this correction.Since practically useful values for M (the number of sections) are 5 to10, and since the maximum allowed overhead for s₂ fields is 5% to 10%,s₂ fields are kept in each subsection shorter than approximately 1% ofthe revolution, or 1% of the circumference of the circular track.

There are several practical approaches for s₂ fields. A correction tablemay be constructed containing one-half track or less shift values foreach subsector divided into 20 radial sub-zones (i.e., this table is Msubsection×20). Following the rule of thumb that a settling time for acontrol system with bandwidth BW is 1/BW, the estimated settling timefor a 3600 rpm patterned media disk is: 0.01×60/3600=166 μs, which wouldrequire at least 6 KHz of bandwidth. This bandwidth is achievable usinga dual-stage actuator employing a MEMS microactuator, and by usinghigher sampling frequency inside S₂ fields.

Referring now to FIG. 5, the present invention also comprises a methodof forming a patterned media disk and a related disk drive architecturefor head positioning. After starting at block 501, one embodiment of themethod comprises creating a portion of a sub-master pattern, asillustrated at block 503. As depicted at block 505, resist is developedand other manufacturing processes are used to create a sub-master basedon the portion of the sub-master pattern, the sub-master comprising onlya section of a full area master. As illustrated at block 507, thesub-master is used as a pattern to form all sections of the full areamaster, and the pattern of the full area master is transferred into amaster substrate (block 509), which can then be used to form one or morereplicas of the master substrate. In addition, a dedicated servo sectionis provided (block 511) that is used for correction of track positioningerrors between sections. The method ends as depicted at block 513.

At block 507, the method may further comprise repeatedly using thesub-master on a surface of the master substrate by rotating thesub-master in a circumferential direction around an axis of the mastersubstrate and by nanoimprinting the sub-master on the master substrate.In addition, the method may further require each section to contain anequal number of servo sectors that are used for head positioning anddata sectors that contain patterned media bits, locating the dedicatedservo sections at a beginning of each section, and providing onededicated servo section for each section to define a plurality ofdedicated servo sections that correct radial, angular, and rotationaltrack positioning errors that are smaller than one-half track width.

In another embodiment, the method may further comprise definingeven-numbered and odd-numbered sections, and nanoimprintingeven-numbered sections first and then transferring a nanoimprintedpolymer pattern into the master substrate by etching or metal lift-off,and nanoimprinting odd-numbered sections into polymer and transferringtheir pattern into the master substrate; and further comprising forminga memory table stored in a ROM in a disk drive for errors present froman inner diameter to an outer diameter of a disk in the disk drive, theerrors being measured relative to base values, which may be defined by afirst nanoimprinted section, to keep a cylinder position in each sectionaccurate by correcting with an error value stored in the memory table.

Referring now to FIG. 6, the present invention also comprises a diskdrive 601 comprising a patterned media disk 603 having a plurality ofdisparate sections 605 arranged circumferentially around a rotationalaxis 607 of the patterned media disk 603. An actuator 609 having a head611 is used for reading data from and/or writing data to the patternedmedia disk 603.

As described above, the disk drive 601 also has a disk drivearchitecture for head positioning having a dedicated servo section thatis used for correction of track positioning errors between sections 605.Each section 605 may contain an equal number of servo sectors for headpositioning and data sectors that contain patterned media bits, and thededicated servo section may be located at a beginning of each section todefine a plurality of dedicated servo sections that correct radial,angular, and rotational track positioning errors that are smaller thanone-half track width. The disk drive may further comprise a memory tablestored in a ROM 613 in the disk drive for errors present from an innerdiameter to an outer diameter of the patterned media disk, the errorsbeing measured relative to base values to keep a cylinder position ineach section accurate by correcting with an error value stored in thememory table.

While the invention has been shown or described in only some of itsforms, it should be apparent to those skilled in the art that it is notso limited, but is susceptible to various changes without departing fromthe scope of the invention.

1. A disk drive, comprising: a patterned media disk having a pluralityof disparate sections arranged circumferentially around a rotationalaxis of the patterned media disk, an actuator having a head for readingdata from and writing data to the patterned media disk; and a disk drivearchitecture for head positioning having a dedicated servo section thatis used for correction of track positioning errors between disparatesections; and wherein each disparate section contains an equal number ofservo sectors for head positioning and data sectors that containpatterned media bits, the dedicated servo section is located at abeginning of each disparate section to define a plurality of dedicatedservo sections that are used to correct radial, angular, and rotationaltrack positioning errors that are smaller than one-half track width. 2.The disk drive as defined in claim 1, further comprising a memory tablestored in a read only memory in the disk drive for errors present froman inner diameter to an outer diameter of the patterned media disk, theerrors being measured relative to base values of an initial one of thedisparate sections to keep a cylinder position in each subsequent one ofthe disparate sections accurate by correcting with a respective errorvalue stored in the memory table.